Print unit activation by means of a clock unit

ABSTRACT

A printing method comprises advancing a media to be printed towards a priming unit of a printing device by means of a media advance unit, detecting a position of the media relative to the printing unit, and providing a corresponding position sensor signal, and activating the printing unit to print on a predetermined portion of the media in accordance with the position sensor signal and a timing signal provided by a clock unit.

BACKGROUND

The disclosure relates to a method and system for activating a printingunit of a printer, in particular for printers with moving pallets,

Some large-scale printers, in particular inkjet primers, are capable ofprinting on bulky and cumbersome printing media, such as corrugatedboards, cardboards, or other large rigid or semi-rigid print substrates.In some of these printers, the printing media is moved on pallets fromthe media loading zone past the printheads towards the media unloadingzone. The pallets that support the media may circulate on an endlesstrack.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of an example of a printing device;

FIG. 2 is a block diagram illustrating components for activating aprinting unit of a printing device in accordance with a position sensorsignal and a timing signal provided by a clock unit in accordance withan example; and

FIG. 3 is a flow diagram that illustrates a printing method in which aprinting unit is activated in accordance with a position sensor signaland a timing signal provided by a clock unit in accordance with anexample.

DETAILED DESCRIPTION

A printing method according to the present disclosure comprisesadvancing a media to be printed towards a printing unit of a printingdevice by means of a media advance unit, detecting a position of saidmedia relative to said printing unit, and providing a correspondingposition sensor signal, and activating said printing unit to print on apredetermined portion of said media in accordance with said positionsensor signal and a timing signal provided by a clock unit.

Activating the printing unit based on said position sensor signal andsaid timing signal provided by said clock unit may allow an accuratesynchronization of the firing of the printheads of the printing unitwith the media position, without the need to rely on feedback from themedia advance unit.

The position sensor signal may provide index information correspondingto a starting position or leading edge of the media or a printing areaon said media or a line to be printed on said media. Based on saidposition sensor signal and based on a known or predetermined velocity atwhich said media advance unit advances said media to be printed, towardssaid printing unit, the printing unit may be activated in accordancewith a timing signal provided by the clock unit, In these examples,neither feedback nor additional position information from the mediaadvance unit is used for activating said printing unit.

The method may hence facilitate the synchronization of the printheadactivation with the media movement, and may contribute to a moreaccurate printing and less complex printing devices.

A printing unit, in the sense of the present disclosure, may denote anyunit adapted to apply printed marks at selected positions on said mediato be printed. In particular, said printing unit may comprise at leastone printhead, such as an inkjet printhead.

In an example, said printing unit may comprise a plurality of printheadscorresponding to printing liquid of different colors, in particular inkof different colors.

A media, in the sense of the present disclosure, may denote anysubstrate on Which printed marks may be applied, including paper,cardboard, corrugated board, or any other material suitable forprinting.

Said timing signal may be an open-loop timing signal.

in the sense of the present disclosure, a clock unit with an open-looptiming signal (as opposed to a closed-loop signal) may be understood todenote a clock unit that is not based on feedback to determine if itsoutput has achieved the desired goal, but merely uses the current stateand an underlying model of the system.

In particular, said timing signal may be independent of feedback fromsaid media advance unit.

In other words, said timing signal may be uncoupled to or independent ofa current position of said media in said printing device.

Activating said printing unit, in the sense of the present disclosure,may comprise triggering said printing unit.

Triggering said printing unit, in an example, may comprise triggering aprinthead of said printing unit to emit printing liquid towards saidmedia to be printed.

Said printing unit may be activated in accordance with a speed at whichsaid media advance unit advances said media towards said printing unit.

Said speed may be a pre-determined speed. Alternatively, said speed maybe a measured speed. The speed may be measured in a one-timemeasurement, and without providing constant feedback. In particular,said speed may be measured with a measurement sensor independent ofand/or uncoupled from said media advance unit.

In an example, said method comprises activating said printing unit toprint on said predetermined, position of said media in accordance withmerely said position sensor signal and said timing signal provided bysaid clock unit and said speed at which said media advance unit,advances said media towards said printing unit.

Said detected position of said media relative to said printing unit maybe an index, such as an edge of said media or the onset of a mediapriming area or line.

In an example, the method further comprises resetting a data pipelinestream for printing on said media in accordance with said positionsensor signal.

Said data pipeline stream may provide or represent the data to beprinted on said media.

Resetting said data pipeline stream in accordance with said positionsensor signal may prevent the system from integrating timing errors thatcould otherwise be generated in an open-loop time-controlled system.

In an example, said media is advanced towards said printhead on aplurality of pallets which trove on a track.

In particular, said track may be an endless track on which said palletscirculate.

A media advance unit based on moving pallets advances the media withhigh spatial accuracy, and hence the firing, of the printhead may bebased on an external clock signal without requiring closed-loop feedbackthat incorporates a detected current media position.

However, the disclosure is not so limited, and one skilled in the artwill appreciate that; the techniques described in the present disclosuremay be applied generally to printing devices of a variety of types,including inkjet and laser printers of various sizes and for variousdifferent purposes.

The disclosure further relates to a printing device, comprising aprinting unit to print on a media, a media advance unit that advancessaid media to be printed towards said printing unit, a sensor unit thatdetects a position of said media relative to said printing unit, andprovides a corresponding position sensor signal, and a clock unit thatprovides a timing signal. Said printing device activates said printingunit to print on it predetermined portion of said media in accordancewith said position sensor signal and said timing signal.

In an example, said clock unit is a free-running clock unit.

A free-running clock unit, in the sense of the present disclosure, maydenote a clock unit that provides a timing signal without relying onfeedback.

In particular, said clock, unit may be physically uncoupled and/ordata-uncoupled from said media advance unit.

In an example, said clock unit comprises an oscillating crystal.Oscillating crystals are known to provide timing signals with highaccuracy in the range of 10 microseconds or better. The timing accuracyof the clock unit directly transfers into a correspondingly high spatialaccuracy with which said printing unit may print on said media.

Said media advance unit may comprise a plurality of pallets forsupporting said media to be printed.

In particular, said pallets may be movable pallets.

In an example, said media advance unit comprises a track on which saidpallets move.

In particular, said track may be an endless track on which said palletscirculate.

Said media advance unit may comprise at east one linear motor for movingsaid pallets, in particular along said track.

Said media advance unit may comprise a plurality of static. magneticelements and a plurality of coils coupled to said pallets.

The disclosure further relates to a computer program or a computerprogram product comprising computer-readable instructions which, whenread on a computing device, in particular a computing device connectedto or incorporated into a printing device with some or all of thefeatures described above, implement a method with some or all of thefeatures described above.

A printing method and printing device in which a printing unit isactivated by means of an external clock unit will now be described ingreater detail with reference to FIGS. 1, 2, and 3 for the specificexample of a large-scale printer with movable pallets. However, thepresent disclosure is not so limited, and applies more generally to avariety of printing methods and printing devices with different mediaadvance mechanisms.

FIG. 1 is a schematic illustration of a printing device 10 in which aprinting unit 12 is triggered to print in accordance with a positionsensor signal 14 provided by a sensor unit 16 and a timing signal 18provided by a clock unit 20. The printing device 10 comprises a mediaadvance unit 22 in which a printing media 24, such as a corrugatedboard, cardboard, or other large rigid or semi-rigid print substrate ismoved from a loading zone 26 past a printing zone 28 that is defined bythe location of the printing unit 12 to an unloading zone 30.

As sketched in FIG. 1, the media advance unit 22 comprises a pluralityof pallets 32 that support the printing media 24. The pallets 32 aremovable along a circular track 34 between the loading zone 26 and theunloading zone 30. For instance, each of the pallets 32 may bebar-shaped, and may be provided with electromagnetic coils at respectiveend portions (not shown), A sinusoidal voltage commutation signal thatmay be generated by a control unit 40 may be supplied to theelectromagnetic coils via brushes from the (static) circular track 34,The circular track 34 may further be provided with static magnets (notshown), which, together with the coils, establish a linear motor thatmay be employed to drive the pallets 32 individually along the circulartrack 34.

The circular track 34 may comprise guide rails (not shown) in which thepallets 32 may move.

Wheel elevators 36 may be employed to transfer the pallets 32 between anupper forward path and a lower return path, as schematically illustratedin FIG. 1.

Alternatively, the pallets may be moving continuously on the endlessrail throughout the forward path and the return path. The linear motorsmay be moved on curved rails by using sophisticated commutationwaveforms.

Each of the pallets 32 may be provided with a plurality of suction holesor recesses (not shown) through which a vacuum source (not shown) mayapply a vacuum force to the underside of the printing media 24, therebyremovably securing the printing media 24 to the pallets 32 for transportthrough the printing zone 28.

Heavy-duty printing devices with moving pallets 32 and transportmechanisms arc described in greater detail in United States patentapplications US 2013/0088554 A1 and US 2013/0170928 A1, to whichreference is made.

The printing unit 12 serves for printing print marks on the printingmedia 24 at predetermined positions. In the configuration illustrated inFIG. 1, the printing unit 12 comprises a plurality of ink printheads 38a to 38 d. For instance, the printheads 38 a to 38 b may correspond tothe four basic colors cyan, magenta, yellow, and black. However, this isjust one example, and any number of printheads may be employed in thecontext of the present disclosure.

As the printing media 24 is inserted into the media advance unit 22 atthe loading zone 26, the sensor unit 16 detects a position of theprinting media 24. For instance, the sensor unit 16 may comprise acapacitive sensor that detects a leading edge of the printing media 24.Alternatively or additionally, the sensor unit 16 may comprise, anoptical sensor that detects a leading edge of the printing media 24, orthe onset of a portion of the printing media 24 on which the printingunit 12 shall print. Information relating to the geometry of theprinting media 24, its lending or trailing edges or the location of aportion of said printing media 24 on which to be printed is sometimesdenoted “index information” in the art. Hence, in other words the sensorunit 16 may detect index information relating to the printing media 24.

The sensor unit 16 sends the position sensor signal 14 relating to theindex information to the control unit 40. The control unit 40 furtherreceives a data stream 42 of information to be printed on the printingmedia 24, such as from an external computing device (not shown).

In general, several mechanisms for moving the pallets are known. A firstimplementation uses electric motors with static coils attached to thetrack and moving magnets attached to the pallets. These systems aresimple to use, and can simultaneously control many pallets with highaccuracy, However, they need to be custom-made and are costly.Alternatively, linear motors with static magnets mounted to the trackand moving coils mounted to the pallets may be employed to drive thepallets, as described above, In the latter systems, an encoder head maybe provided on each side of the moving pallet, and the encoder signalsused to synchronize the printhead fire pulse to the movement of themedia. However, the number of encoders in a given printing device may beconsiderable, and hence many corresponding encoder signals exist.Depending on the position of the pallets, each time another signal needsto be used for data pipeline synchronization. The encoder signals fromthe moving encoders can be sinusoidal signals or high frequency digitalsignals. Both types of signals are easily disturbed when they are pickedup from the moving encoders, such as through sliding brushes.

In a known printing device such as described in US 2013/0088554 A1 or US201310170928 A1, the fire timing of the inkjet printheads 38 a to 38 dis synchronized with the media movement by means of rotary encoderscoupled to the pellets.

In contrast, the printing device 10 illustrated in FIG. 1 comprises aclock unit 20, such as a clock unit comprising an oscillating crystalthat may provide a timing signal 18 to the control unit 40 with highprecision in the microsecond range.

Based on the index position sensor signal 14, the timing signal 18, andthe known velocity at which the pellets 32 (and hence the printing media24) move in the media advance unit 22, the control unit 40 may determinethe precise timing at which the portions of the printing media 24 onwhich the data stream 42 shall be printed reach the respectiveprintheads 38 a to 38 d, and may provide the respective print triggersignals 44 to the printing, unit 12. Hence, the information pertainingto the data stream 42 may be printed at the pre-defined positions of theprinting media 24 with high timing accuracy, and hence high spatialaccuracy.

As can be taken from FIG. 1, the clock unit 20 may be an external clockunit that provides an open-loop timing signal unrelated, to the mediaadvance movement in the media advance unit 22, and in particularunrelated to or independent of position feedback from the pellets 32.The position sensor signal 14 provided by the sensor unit 16 may merelyserve as a media entry sensor to trigger the clock unit 20, but need notprovide constant or repeated information on the position of the printingmedia 24 as the printing media 24 advances towards and through theprinting zone 28. In particular, the position sensor signal 14 may beunrelated to the current positions of the pellets 32.

The control unit 40 may employ the position sensor signal 14 as a resetsignal to reset the data pipeline clocking of the data stream 42,thereby preventing the system from integrating timing errors that couldotherwise accumulate in the open loop control, and hence furtherenhancing the printing accuracy.

The clock unit 20 is shown in FIG. 1 as an external unit. However, thisis merely an example, and in sonic implementations the clock unit 20 maybe incorporated into the control unit 40.

In some examples, the media advance unit 22 comprises a clock unit forcontrolling the media advance movement, in particular the movement ofthe pellets 32. in these configurations, the same clock unit may providethe timing signal 18 for the control unit 40 and for the media advancemovement.

FIG. 2 is a schematic view of some of the components of a printingdevice according to an example of the present disclosure, and inparticular illustrates an example for the data handling in the controlunit 40.

As described above in more detail with reference to FIG. 1, the sensorunit 16 provides a position sensor signal 14 corresponding to indexinformation of the printing media 24. The external clock unit 20provides the timing signal 18. The control unit 40 comprises a clockgenerator unit 46 that receives the timing signal 18 from the externalclock unit 20 and is triggered or reset by the position sensor signal 14received from the sensor unit 16, thereby synchronizing the control unit40 to the index information of the printing media 24 inserted into theloading zone 26.

The control unit 40 further comprises a data processing unit 48 whichreceives the clock and index information from the clock generator unit46, and further receives the data stream 42 containing the informationto be printed, and based on this input generates the print triggersignals 44 for the printheads 38 a to 38 d.

FIG. 3 is a flow diagram for illustrating a method according to anexample of the present disclosure, such as for printing with theprinting devices illustrated in FIG. 1 or 2.

In S10, the printing media 24 to be printed is advanced towards theprinting unit 12 of the printing device 10 by means of the media advanceunit 22.

In S12, a position of said printing media 24 relative to said printingunit 12 is detected, and a corresponding position sensor signal 14 isprovided, such as to a control unit 40.

S10 and S12 may be executed concurrently, or sequentially.

In S14, said printing unit 12 is activated, to print on a predeterminedportion of said printing media 24 in accordance with said positionsensor signal 14 and a timing signal 18 provided by a clock unit 20.

The open loop timing approach of the present disclosure may greatlysimplify the system structure of the printing device, and may enableprinting systems with high precision based on relatively low cost staticmagnets and moving coils linear motors.

The description of the examples and the figures merely serve toillustrate the disclosure, but should not be understood to imply anylimitation. The scope of the disclosure is to be determined based on theappended claims.

REFERENCE SIGNS

-   10 printing device-   12 printing unit-   14 position sensor signal-   16 sensor unit-   18 timing signal-   20 clock unit-   22 media advance unit-   24 printing media-   26 loading zone-   28 printing zone-   30 unloading zone-   32 pallets-   34 circular track-   36 wheel elevators-   38 a-38 d printheads of printing unit 12-   40 control unit-   42 data stream-   44 print trigger signals-   46 clock generator unit-   48 data processing unit

1. A printing method, comprising: advancing a media to be printedtowards a printing unit of a printing device by means of a media advanceunit; detecting a position of said media relative to said printing unit,and providing a corresponding position sensor signal; and activatingsaid printing unit to print on a predetermined portion of said media inaccordance with said position sensor signal and a timing signal providedby a dock unit.
 2. The method according to claim 1, wherein said timingsignal is an open-loop timing signal.
 3. The method according to any ofthe preceding claims, wherein said timing signal is independent offeedback from said media advance unit.
 4. The method according to any ofthe preceding claims, wherein said printing unit is activated inaccordance with a speed at which said media advance unit advances saidmedia towards said printing unit. 5, The method according to any of thepreceding claims, further comprising: resetting a data pipeline streamfor printing on said media in accordance with said position sensorsignal.
 6. The method according to any of the preceding claims, whereinsaid media is advanced towards said priming unit on a plurality ofpallets which move on a track, in particular on an endless track.
 7. Aprinting device, comprising: a printing unit to print on a media; amedia advance unit that advances said media to be printed towards saidprinting unit; a sensor unit that detects a position of said mediarelative to said printing unit, and provides a corresponding positionsensor signal; and a clock unit that provides a timing signal; whereinsaid printing device activates said printing unit to print on apredetermined portion of said media in accordance with said positionsensor signal and said timing signal.
 8. The printing device accordingto claim 7, wherein said clock unit is a free-running clock unit.
 9. Theprinting device according to claim 7 or 8, wherein said clock unit isuncoupled from said media advance unit.
 10. The printing deviceaccording to any of the claims 7 to 9, wherein said clock unit comprisesan oscillating crystal.
 11. The printing device according to any of theclaims 7 to 10, wherein said media advance unit comprises a plurality ofpallets for supporting said media to be printed, in particular aplurality of movable pallets.
 12. The printing device according to claim11, wherein said media advance unit comprises a track on which saidpallets move, in particular an endless track.
 13. The printing deviceaccording to claim 11 or 12, wherein said media advance unit comprisesat least one linear motor for moving said pallets.
 14. The printingdevice according to any of the claims 11 to 13, wherein said mediaadvance unit comprises a plurality of static magnetic elements and aplurality of coils coupled to said pallets.
 15. A computer programproduct comprising computer-readable instructions which, when read on acomputing device, implement a method according to any of the claims 1 to6.